1. Field of the Invention
This invention relates generally to irrigation water sprinklers of the type having a rotatable sprinkler spray head. More specifically, this invention relates to such sprinklers having oppositely rotating sprinkler head drive elements and a mechanism for selectively driving the sprinkler head alternately by the drive elements to produce oscillating rotation.
2. Related Art
Rotary sprinklers are typically driven in rotation by the force of water exiting a spray head or by an impeller inside the sprinkler through which water passes. In the latter case, the impeller rotates at a higher speed than the spray head. The impeller then is used to drive a speed reducing transmission that in turn drives the spray head.
Typical sprinkler drive systems thus include a rotating shaft that rotates the spray head. This is effective for rotating the spray head continuously in one direction. However, where it is desired to have the spray head oscillate through a defined arc of less than 360.degree., it is necessary to be able to reverse the direction of rotation of the spray head.
One method that has been used for doing this is to use a gear rotating on a shaft, which gear drives two different gear trains, all supported on a single plate. Typically a yoke assembly supporting the gear trains is shiftable for alternately engaging a terminal gear from each drive train with a gear driving the spray head. An example of such construction is disclosed in U.S. Pat. No. 4,568,024 issued to Hunter.
It has been found that substantial force is required to disengage a terminal gear and shift to the opposite direction. It is therefore desirable to have a sprinkler transmission that provides drive off of a large radius drive gear, such as a ring gear, to reduce the force applied to teeth of the drive gear. Further, it is desirable to have a sprinkler transmission that provides oppositely rotating elements that may be engaged alternatingly to drive the spray head in reciprocal directions.